Immersion-Controlled Nanoparticle Electrodeposition on a Patterned Pyrolyzed Photoresist Film Electrode for Single-Entity Electrochemistry Studies Using Scanning Electrochemical Cell Microscopy.

We report immersion-controlled electrodeposition as a simple means to fabricate a substrate with defined zones of differently sized nanoparticles and demonstrate its application in scanning electrochemical cell microscopy (SECCM) studies. Defined zones were formed via electrodeposition accompanied by stepwise increases in the immersion depth of a vertically oriented substrate electrode. In this study, the method was demonstrated for the cathodic deposition of platinum nanoparticles (PtNPs) on a pyrolyzed photoresist film (PPF) electrode with a comb-shaped pattern. The sizes and surface immobilization density of PtNPs were measured by scanning electron microscopy, and currents from the hydrogen evolution reaction (HER) in 0.1 M HClO4 were measured in each zone by SECCM. The stepwise deposition via cyclic voltammetry enabled reproducible formation of distinct zones decorated with well-separated PtNPs of controlled sizes (10-50 nm in radius). The resulting PPF substrate was suitable for single-entity SECCM measurements, showing HER current proportional to the number of PtNPs in an SECCM droplet and a correlation between HER activity and PtNP size.